The present invention pertains generally to electroactive materials and in particular to organic polymeric conductive materials.
Presently, numerous metals and other inorganic substances are used to fabricate electrical conductors, semiconductors, electronic devices, and electromagnetic or acoustic sensors. The utility of these materials is frequently limited by such factors as weight, mechanical fragility, fabrication problems, corrosion, scarcity, and high costs.
Many organic materials have properties which overcome or minimize these problems and possess several other advantages, such as ease of fabrication into films, filaments, and complex shapes and variability in molecular design. Of particular importance is the possibility with organic materials to fabricate electronic devices whose dimensions are "molecular", such as diodes, capacitors, and gates whose dimensions are in the range of 10 A to 500 A.
Numerous resinous compositions that conduct electricity are known. Many of them comprise an organic resin with a conductive material, e.g., a metal or graphite, dispersed in a resin. Due to a lack of chemical bonding and the discreteness of the conductive filler, the mechanical properties are not good and loading the polymeric binder with sufficient filler to produce a polymeric conductor with sufficient conductivity to meet the requirements of many applications is often not possible. Further, metallic corrosion can deteriorate the conductivity of the composition. Metals and graphite are not transparent and their inclusion prevents the fabrication of a transparent conductor.
One type of conductive resin includes radical-anion salts of 7,7,8,8-tetracyanoquinodimethane (TCNQ) which are themselves organic semiconductors. A complex salt, M.sup.+ (TCNQ).sub.2.sup. , is also used and is preferred on account of a higher conductivity than the corresponding simple salt, M.sup.+ TCNQ.sup. . The properties of polymeric semiconductors of the polycation-TCNQ type have some advantages over their monomeric derivatives in that they are processable and their conductivity can be controlled by varying the TCNQ concentration. However, the matrix polymer is brittle due to its ionic nature, and its stability is lowered by sensitivity to moisture. Another approach is to disperse TCNQ salts into non-ionic matrix polymers so that advantage can be taken of the mechanical properties and higher stabilities of the polymer; however, compatibility, stability, and dispersion problems still remain.